1. Field of the Invention
The present invention relates to a lumbar support device in an automotive seat, and in particular to a lumbar support device which is provided in the seat back of automotive seat to support the lumbar part of an occupant sitting on the seat in order to alleviate his or her fatigue.
2. Description of Prior Art
Conventionally, a typical construction of lumbar support device in the seat back of automotive seat has been such that a lumbar plate is disposed movably between both lateral frame sections of a seat back frame, at a point corresponding to the lower area of the seat back suited for supporting the lumbar part of an occupant sitting on the seat, and that a drive mechanism is mounted on the seat back frame, the drive mechanism having a rod extending inwardly of the seat back frame, on which rod is provided that lumbar plate. Operation of the drive mechanism causes the lumbar plate to be moved forwardly and backwardly of the seat back frame via the rod. Thus, such movement of the lumbar plate gives and releases a pressure against a lumbar support area of foam cushion member in the seat back, so that the occupant may adjust the soft or hard cushiony degree of that particular lumbar support area to vary a support pressure of foam cushion member as desired against his or her lumbar part. This is disclosed, for instance, from the U.S Pat. Nos. 4,886,316 and 5,174,629
However, the lumbar plate itself is formed from a hard metallic plate and occupies small area relative to the whole area of frontal surface of the seat back. Consequently, the prior-art lumbar support device has been found defective in that the lower part of the foam cushion member is only applied a constant pressure by the flat surface of lumber plate, resulting in hardening only the lower lumbar support area of cushion member, without applying any pressure to other area of the cushion member than that lower lumbar support area , particularly an upper area of the same thereabove. Such non-pressed area of cushion member remains soft and raises the problem of unstable pressure distribution around the lumbar support area of seat back, for which reason, the occupant can not attain an optimal pressure distribution at the lumbar support area of seat back according to his or her own weight and has felt uncomfortable with this conventional lumbar support way.